1. Field of the Invention
The invention relates to an agitator mill comprising a grinding receptacle enclosing a grinding chamber, an agitator unit rotatably disposed in the grinding chamber concentrically of the latter's axis, a drive motor coupled with the agitator unit, a grinding-stock/auxiliary-grinding-body discharge line leading out of the grinding chamber, a grinding-stock/auxiliary-grinding-body separator device separate from the agitator mill and connected to the discharge line, a grinding-stock supply and auxiliary-grinding-body return line connected to the separator device and a grinding-stock supply line on the one hand, and to the grinding chamber on the other, and a grinding-stock pump arranged in the grinding-stock supply line.
2. Background Art
An agitator mill of the generic type is known from DE 30 38 794 A1, in which the milled grinding stock and the auxiliary grinding bodies are removed from the grinding chamber by means of a worm conveyor and supplied to a riddler as a separator device. The riddler serves to isolate the grinding stock and auxiliary grinding bodies that have become too small and scraps of auxiliary grinding bodies; the auxiliary grinding bodies of sufficient size are supplied to a mixing hopper, to which grinding stock to be processed is supplied by means of a grinding-stock pump. The grinding stock to be processed and the auxiliary grinding bodies are supplied as a mix via a line to another worm conveyor that feeds this mix into the agitator mill. It is the purpose of these measures that a given pressure in the grinding chamber be maintained. Affecting the pressure in the grinding chamber is to become possible through modifications of the speed of the worm conveyors before the grinding chamber inlet and behind the grinding chamber outlet. This does not help achieve high grinding-stock throughputs.
An agitator mill is known from U.S. Pat. No. 4,496,106, in which the auxiliary-grinding-body return line opens into the grinding-stock supply line by an angle of 90.degree. directly before the grinding-stock/auxiliary-grinding-body inlet. As a result of the centrifugal effect produced by the agitator unit, the auxiliary grinding bodies and grinding stock not sufficiently milled are to be catapulted off through the auxiliary-grinding body outlet and returned through the grinding-body return line. By the grinding-body return line opening into the grinding-stock supply line, a suction is to be generated, still supporting the centrifugal effect. Further, excellent preliminary mixing of the grinding stock and the auxiliary grinding bodies is to result in the grinding-stock supply line. Experience has shown that any reliable circulation of the auxiliary grinding bodies cannot be ensured by this design of the known agitator mill. The auxiliary grinding bodies get stuck in the auxiliary-grinding-body return line, where they stay. Although, owing to their basic concept, agitator mills of this type have considerable advantages where a high throughput of grinding stock is required that is marked by a considerable transport of auxiliary grinding bodies in the grinding chamber to the separator device, this type of agitator mills has not been successful in practice, because the circulation of the auxiliary grinding bodies does not work.
U.S. Pat. No. 2,595,117 discloses a dry-milling ball mill. In this ball mill, the milled grinding stock and the grinding bodies are removed in common through a discharge line and placed into a vertical air duct that serves as an air separator. Air is blown from below through this vertical air duct, transporting all the smaller particles into a separator. The grinding balls and the coarse fraction of the grinding stock will fall downwards through the duct against the air stream and are returned to the mill via a conveyor worm. In the separator, sufficiently fine material is once again separated from the grinding stock not sufficiently milled. The latter is likewise fed to the worm via a line.
An agitator mill is known from EP 0 146 852 B1, comprising a grinding receptacle with a cylindrical inner wall and a cylindrical agitator unit, a grinding chamber being formed between the agitator unit and the inner wall of the grinding receptacle. On its free end, the agitator unit has a cavity, into which projects a separator device. In this area, the agitator unit is provided with recesses all around the separator device, the recesses allowing the auxiliary grinding bodies, which reach the cavity from the front of the free end of the shaft, to be discharged radially into the adjacent grinding chamber. There is the risk of auxiliary grinding bodies compacting in the vicinity of the free shaft end, i.e. around the cavity.